The Campaign to Protect Rural England (CPRE) said that 20 large housing schemes on “open countryside” had been allowed to proceed, despite being formally opposed by local authorities.

The organisation said that it was “deeply disturbed” by the impact of the planning reforms which was leaving local communities “increasingly powerless”.

Ministers last year introduced the National Planning Policy Framework (NPPF) to streamline the laws and encourage more development. Councils are required to draw up plans for housing and development or face having to allow any project deemed to be “sustainable development”.

The Telegraph’s “hands off our land” campaign urged the Government to show restraint, but dozens of councils have failed to put in place adequate plans and evidence is emerging of developments being forced through against local wishes. Housing developments were a significant issue in the recent Eastleigh by-election with Conservatives and Liberal Democrats accusing one another of allowing unsuitable local projects.

The CPRE also highlighted the approval of almost 300 homes on greenfield sites on the edge of Tetbury in the Cotswolds Area of Outstanding Natural Beauty and on prime farmland.

Shaun Spiers, the organisation’s chief executive, said: “CPRE has closely observed how the NPPF is being implemented on the ground and what we have seen is deeply disturbing. Despite the rhetoric of localism, it now seems that local communities are increasingly powerless to prevent damaging development even in the most sensitive locations.”

He added: “Our evidence suggests that the NPPF is being used to impose unnecessary greenfield developments in the teeth of local opposition.”

The CPRE’s analysis also found that despite government assurances that protected areas of landscape and the green belt would be safe from building, urban development was “implicitly” being encouraged on such land.

In an interview with The Sunday Times, Mark Prisk, the housing minister, indicated that there might be situations when development on green belt land was acceptable.

“If there was evidence that it was previously used as industrial land, then locally councils could consider building on brownfield land in the green belt – councils already do that,” he said.

“We need to encourage redevelopment … [but] any open space built on would have to be replaced somewhere else.”

The Government has strongly defended the reforms and is expected to call for more housing development in this week’s Budget. A spokesman for the Communities Department said: “The framework is clear that very strong protections are in place to safeguard the green belt and protect other areas, such as Areas of Outstanding Natural Beauty.

“There have been more than 2,300 major residential decisions made through the planning system since the introduction of the framework and to focus on just tens of cases and claim they are in some way representative is not credible.”